Ionization detectors for gas chromatography are well known in the art. A comprehensive survey of such detectors as of 1961 may be found in an article entitled "Ionization Methods for the Analysis of Gases and Vapors" by J. E. Lovelock, Analytical Chemistry, Volume 33, No. 2, February 1961, pages 162-178. The detectors reviewed in that article include, inter alia, the cross-section ionization detector, the argon detector, and the electron capture detector. These detectors are characterized by the fact that each includes a source of ionizing radiation, i.e., a radioactive material.
The use of radioactive substances in chromatographic detectors necessarily introduces certain health risks into the laboratory and complicates such tasks as cleaning detectors after use. Because of these health risks, they are also subject to certain governmental controls which complicate their application and use.
Ionization detectors have been developed which avoid the need for radioactive elements. However, in many cases, these are not suitable for use as argon and electron capture detectors for various reasons, including the fact that they may require gases other than the carrier or sample. Examples are the photo-ionization detector referenced in the above-mentioned Lovelock article and the flame ionization detector.
More recently, an electron capture detector has been developed which utilizes a thermionic emission electron source. Such a detector is described in U.S. Pat. No. 4,304,997 of Sullivan et al. However, there are certain problems inherent in a thermionic detector. One such problem is that the emitting filament may be "poisoned" by components of many samples--i.e., components may be adsorbed on the surface and thereby reduce its thermal emission.
For the foregoing reasons, it would be desirable to provide an ionization detector which would avoid the use of ionizing radiation, additional gases, and heated filaments.